This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit

Jastrzebski, J.

Karwowski, H.

Sadler, M.

Sarantites, D.G.

Singh, P.P.

Westerberg, L.

Wiggins, J.

English

IUScholarWorks

MULTIPLICITY OF GAMMA-RAY TRANSITIONS OBSERVED I N  LITHIUM-INDUCED REACTIONS 
H. Karwowski,* P.P. Singh, J .  Wiggins, M. ~ a d l e r , * *  J. ~ a s t r z e b s k i , *  
D .G. ~ a r a n t i t e s  ,t and L. westerberg+ 
The m u l t i p l i c i t i e s  of t he  y-rays observed i n  
6 ~ i  bombardment of 5 6 ~ e ,  1 6 5 ~ 0  and t a r g e t s  
have been measured using the  de t ec to r  system 
des cr ibed  elsewhere. '9 2, These s tudies  were under- 
taken t o  augment our understanding of t h e  mechanism 
of the l i t h ium induced r eac t ions  which had e a r l i e r 3 )  
been s tudied  a t  IUCF through (a) energy dependence 
of t he  production cross  s ec t ions  of var ious  f i n a l  
n u c l e i  determined by inc lus ive  y -ray technique 
and (b) t he  sys temat ics  of t he  r e c o i l  ranges,  both 
i n t e g r a l  and d i f f e r e n t i a l ,  of  t he  f i n a l  nuc l e i .  
Fig. 1 shows t y p i c a l  zero-, one-, two- and 
three-fold Ge(Li) de t ec to r  s p e c t r a  f o r  t he  case of 
the 165~o  t a r g e t  bombarded wi th  66 MeV 6 ~ i  pro- 
j e c t i l e s .  y-ray t r a n s i t i o n s  which have t h e  h ighes t  
m u l t i p l i c i t y  s tand  ou t  more d i s t i n c t l y  above the  
background i n  t h e  higher-fold spectrum r e l a t i v e  t o  
those of lower m u l t i p l i c i t y .  From these  d a t a  t he  
average m u l t i p l i c i t i e s  a s  we l l  a s  t h e  h igher  mo- 
ments of i ts d i s t r i b u t i o n s  have been ex t r ac t ed  
using two techniques. The energies  and t h e  multi- 
p l i c i t i e s  of t he  r e l a t i v e l y  i n t e n s e  gamma rays  
and the  t r a n s i t i o n s  t h a t  they correspond t o  a r e  
given f o r  a r ep re sen ta t i ve  s e t  of f i n a l  n u c l e i  
produced wi th  t he  5 6 ~ e  t a r g e t  i n  Table 1 and wi th  
t he  165~0 t a r g e t  i n  Table 2. For comparison i t  is 
worth not ing  he re  t h a t  t he  average angular  momentum 
t r ans fe r r ed  t o  t he  compound nucleus by the  i nc iden t  
6 ~ i - p r o j e c t i l e  is 22 li and 16 11 f o r  t he  l65Ho and 
5 6 ~ e  t a r g e t  nuc l e i ,  r e spec t ive ly .  
The y-rays t r a n s i t i o n s  which belong t o  t he  
highest-Z n u c l e i  produced i n  t he  6 ~ i  bombardment 
a r e ,  f o r  example 5%i with  the  5 6 ~ e  t a r g e t  and 
with  the  165~0  t a r g e t ,  found t o  have the  
h ighes t  m u l t i p l i c i t y ,  the  values f o r  which a r e  
cons i s t en t  wi th  (assuming t h e  y - t r ans i t i ons  a r e  
quadrupole i n  na tu re )  t he  average angular  momentum 
t r ans fe r r ed  t o  t he  compound nucleus (see Table 1 
and 2 ) .  On t he  o the r  hand it  is i n t e r e s t i n g  t o  
note ,  e spec i a l l y  f o r  t r a n s i t i o n s  i n  1 6 5 ~ m  and 
164~r  n u c l e i  produced wi th  t he  1 6 5 ~ 0  t a r g e t ,  t h a t  
t he  m u l t i p l i c i t y  of t he  t r a n s i t i o n s  among the  
lower l y ing  and lower J s t a t e s  is not iceably  
smal ler  (on an average 4-5 vs. 8-10) than those 
o r ig ina t ing  from higher  l y ing  (and h igher  J )  
s t a t e s .  This p a t t e r n  can only be understood i f  
t he  lower energy s t a t e s  bes ides  being populated 
from the  h igher  l y i n g  s t a t e s  through y-cascade 
a r e  a l s o  being populated independently by another 
process.  I f  a 1  and 02 a r e  t he  cross  s ec t ions  
wi th  which the  two processes con t r ibu t e  t o  t h e  
populat ion of  t he  lower l y ing  s t a t e s  and M1 and 
M2 a r e  t he  average m u l t i p l i c i t i e s  due t o  each of 
t he  two processes,  r e spec t ive ly ,  then t h e  observed 
m u l t i p l i c i t y  of  t he  t r a n s i t i o n s  from the  lower 
l y i n g  s t a t e s  w i l l  be 
t llli ' ~ i  +'"Ho, E,, = 66 MeV 
Table 1. y-Ray M u l t i p l i c i t i e s  Observed i n  6 ~ i  + Table 2. !-Ray M u l t i p l i c i t i e s  Observed i n  6 ~ i  + 
56Fe Reaction a t  66 MeV Bombarding Energy 6 5 ~ 0  Reaction a t  66 MeV Bombarding 
Energy 
Nucleus Ey Trans i t ion  < M> Nucleus E y T rans i t i on  < M> 
being populated by a mechanism which t r a n s f e r s  
5 2 ~ r  1434.3 2+ -+ O+ 5.8 r e l a t i v e l y  lower angular  momentum t o  t he  f i n a l  
935.5 4+ + 2+ 6.4 
1334 .O 41+ + 2' 6.7 system. Using the  observed i n t e n s i t i e s  of t he  
y-rays i t  is es t imated  t h a t ,  both f o r  1 6 5 ~ m  and 
Experimental e r r o r s  i n  t he  va lues  of <M> quoted 
i n  Tables 1 and 2 a r e  about 20%. 164~r,  whereas t h e  m u l t i p l i c i t y  of  t he  h igher  
t r a n s i t i o n  is  of t h e  order  of 8-10 t h a t  of  t he  
The f a c t  t h a t  t he  observed m u l t i p l i c i t y  of  t he  process feeding the  lower s t a t e s  only is about 4.  
t r a n s i t i o n s  among the  lower l y ing  s t a t e s  is s ign i -  Recently i n  another experiment i n  progress 
f i c a n t l y  less than t h a t  of t r a n s i t i o n s  among t h e  a t  IUCF,~)  i t  has been observed t h a t  (a) the  par- 
h igher  s t a t e s  impl ies  t h a t  lower l y ing  s t a t e s  a r e  a h  t i c l e  s p e c t r a  fol lowing 6 ~ i  bombardment of l g 7 ~ u  
and 5 6 ~ e  a r e  charac ter ized  by broad a and d peaks 
wi th  energy corresponding t o  t he  beam v e l o c i t y  and 
(b) t h a t  t he  y-rays i n  coincidence wi th  t he  beam 
v e l o c i t y  a [ o r  d l  have the  f e a t u r e  a s  i f  those y-rays 
were produced by (d,xn) [o r  (a ,xn) 1 type reac t ions .  
These r e s u l t s  a r e  being i n t e r p r e t e d  a s  i f  t h e  i nc i -  
dent  6 ~ i  p r o j e c t i l e  d i s s o c i a t e s  i n  t he  f i e l d  of  a 
nucleus i n t o  an a fragment and a deuteron fragment 
which i n  t u r n  i n t e r a c t  wi th  t h e  same nucleus pro- 
ducing, among o t h e r  th ings ,  (d,xny) and (a,xny) 
r eac t ions .  I f  t h i s  p i c t u r e  were t r u e  then i t  must 
show up a s  h igher  m u l t i p l i c i t y  f o r  those  y-rays 
which a r e  produced fol lowing the  fus ion  of  6 ~ i  
p r o j e c t i l e  wi th  t he  t a r g e t  nucleus and lower mult i-  
p l i c i t y  f o r  those which a r e  produced fol lowing t h e  
fus ion  of  a -pa r t i c l e  wi th  t he  t a r g e t  nucleus.  It 
is i n t e r e s t i n g  t o  compare t he  two types of observed 
m u l t i p l i c i t i e s  wi th  t he  average amount of angular  
momentum t h a t  t he  fus ion  of beam v e l o c i t y  6 ~ i ,  a 
and d can t r a n s f e r  t o  t h e  compound nucleus. These 
va lues  a r e  about 22, 12  and 7 li u n i t s ,  r e spec t ive ly .  
Note t h a t ,  f o r  example, <M> of 8-10 and 4 f o r  t he  
two mechanisms correspond t o  average J i n  165Th and 
164~r,  before  y decay s t a r t e d ,  of 16-20 and 8 R 
u n i t s  (assuming t h a t  t h e  average mu l t i po l a r i t y  of 
t he  y-rays i n  quadrupole). The proximity of  t he  
average J deduced from the  two va lues  of t h e  mult i-  
6 p l i c i t y  t o  those  t r a n s f e r r e d  by L i  and the  beam 
v e l o c i t y  a lpha  (or  d) g ive  credence t o  t he  above 
p i c tu re .  I n  o t h e r  words, t h e  h igher  sp in  s t a t e s  i n  
1 6 5 ~ m  and 164~r a r e  produced fol lowing the  nuc l ea r  
evaporat ion from the  l7'Yb compound nucleus 
formed by fus ion  of 6 ~ i  with  165~0  whi le  t he  low 
ly ing  s t a t e s  a r e  a l s o  produced fol lowing t h e  nu- 
cleon evaporat ion from 1 6 9 ~ m  formed by the  process 
of  t he  beam v e l o c i t y  a wi th  t he  165~o. The former 
i s  a h igher  m u l t i p l i c i t y  while t he  l a t t e r  is a 
lower m u l t i p l i c i t y  process.  From t h e  observed 
cross  s e c t i o n s  i t  can a l s o  be concluded, i f  t h i s  
were t he  case ,  t h a t  1 6 5 ~ m  is  produced about twice 
a s  s t rong ly  by the  l a t t e r  process  than by the  
former one. 
Though f u r t h e r  ana lys i s  of  d a t a  is  needed 
t o  be s u r e  t h a t  t he  above r e s u l t s  and conclusions 
a r e  v a l i d ,  i t  is obvious, however, t h a t  t h e  mult i-  
p l i c i t y  information can be u se fu l  i n  i d e n t i f y i n g  
and determining t h e  ex t en t  t o  which d i f f e r e n t  
processes may be con t r ibu t ing  i n  t he  production 
of  a nucleus i n  a given nuclear  r eac t ion .  
* Permanent address : INR, Swierk , Poland 
**present address: Physics Department, UCLA, 
Los Angeles, CA 90024 
+washington Univers i ty ,  S t .  Louis, MO 63130 
1 )  D.G. S a r a n t i t e s  e t  a l . ,  Phys. Rev. G, 
2138 (1976). 
2) IUCF Annual Report, 1977, page 77. 
3) IUCF Annual Report, 1977, p. 73 and t h i s  
r epo r t  p. 128. 
4) t h i s  r epo r t  p. 134. 


Multiplicity of Gamma-Ray Transitions Observed in Lithium-Induced Reactions

https://scholarworks.iu.edu/dspace/bitstream/2022/3010/1/iucf_1977_143-146.pdf

Multiplicity of Gamma-Ray Transitions Observed in Lithium-Induced Reactions

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